Multi-stage burner unit



Nov. 8, 1966 R. c. FARNHAM 3,283,802

MULTI-STAGE BURNER UNIT Filed June 11, 1964 2 Sheets-Sheet 1 Inventor: $76 oa Vela: Far 1/9 y i m Nov. 8, 1966 R. c. FARNHAM 3,283,802

MULTI-STAGE BURNER UNI T Filed June 11, 1964 2 Sheets-Sheet. 2

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Inventors 1P5)! fours/4's firnfiab? United States Patent 3,283,802 MULTI-STAGE BURNER UNIT Rex Couvelas Farnham, Cookham Dean, England, as-

signor to Fuel Firing Limited, Reading, England, a British company Filed June 11, 1964, Ser. No. 374,380 8 Qlaims. (Cl. 1581.5)

The invention relates to multi-stage burner units for liquid, gaseous and pulverized fuels.

High efliciency combustion of fuel in a boiler or other furnace is generally effected with pressure jet atomization of the fuel. When a liquid fuel is being used for high output, say for the combustion of up to about eight tons, or more, of fuel per hour, the nozzle of the burner is of such size as to require the fuel oil to be fed to the burner at very high pressure, for example, up to 2000 lbs. per square inch. This involves high outlay on pumps, piping, heaters and other ancillary parts.

It is an object of the invention to provide a burner unit capable of high output in which such disadvantages are mitigated.

An object of the present invention is to provide a burner unit comprising a plurality of individual stages arranged in a cluster in a housing common thereto and retractable from a furnace wall adapted slidingly to receive the unit in order to cut off supply of air to the unit, each stage including an air duct for combustion air connected to a pressure source of combustion air common to all stages, a burner within and surrounded by each duct and having associated therewith a sprayer for fuel connected to a source of fuel common to all stages, and means in each duct and about each burner for effecting turbulence of combustion air in such wise that air from one duct is rotated in' a direction opposite to that imparted to air from an adjacent duct.

The cluster of stages can in operation be considered as a single burner unit, whether the individual nozzles of the stages are integrally connected together or not.

The number of individual nozzles in the cluster may be varied as required. The atomizers or sprayers of the individual burners are connected or coupled to a single supply of fuel, for example, oil, gas or pulverized fuel, and the air fed through the swirlers, or other means for supplying the correct quantity of air at the correct velocity and in the correct direction, of the individual stages is derived from a common pressure source or reservoir. The fuel is fed to the burner unit as a whole through a single inlet and the air to said burner unit is likewise fed through a single inlet or from a single reservoir or wind box. The burner unit may then be readily operated at a pressure which is normally used in a conventional pressure jet burner, for example, about 450 lbs. per sq. inch. High outputs, for example the combustion of up to eight tons or more of fuel per hour, may be readily achieved with a suitably sized burner unit as a whole without the necessity of providing high pressure pumps, heaters and piping effective to withstand the high presures.

The individual stages may be of the kind which do not require refractory quarls, for example burners of the kind illustrated in U.S. Patent No. 2,911,034. It will, however, be understood that the cluster of stages according to the invention can be used with refractory quarls.

The multi-stage burner unit permits flame monitoring to be applied between the stages, that is, within the flame itself and enables monitoring for ignition to be applied between the stages. The individual stages are so arranged in the cluster that the combustion in one stage assists the combustion in another stage, although each stage is itself self-supporting.

The burner unit as a whole provides two or morei streams of fuel each provided with its own supply of air and all combined in one unit. This permits better mixing and proportioning to be achieved so enabling more eflicient combustion to be attained.

The swirlers or other means employed to create turbulence are provided to give the air or the air and fuel of each stage rotation about the longitudinal axis of the stage in an opposite direction to that of the adjacent stage. This enhances the degree of turbulence which in turn assists rapid combustion and a high rate of heat release, a very useful advantage particularly in fully cooled furnaces.

The invention is diagrammatically illustrated by Way of example only in the accompanying drawings, in which:

FIG. 1 is a front view of a multi-stage fuel burner unit according to the invention;

FIG, 2 is a cross section through the unit shown in FIG. 1; and

FIG. 3 is a front view of another multi-stage fuel burner unit according to the invention.

The burner unit 31 shown in FIGS. 1 and 2 comprises three stages 32 mounted in a housing 33 of circular cross section slidable in a furnace wall 40. Each stage 32 comprises a burner tube 34 mounted coaxially within a combustion air duct and surrounded at its forward or nozzle end 34a by a sleeve 35 provided with longitudinal slots, and swirlers 36 for secondary air mounted at the forward end of the sleeve 35 to swirl the air for combustion supplied from a pressure source to swirl the air for combustion supplied from a pressure source and passing through the duct about the longitudinal axis of the burner tube. One of the swirlers 36 is provided to rotate the secondary air in a direction opposite to that imparted to the secondary air passing through the two other swirlers. The nozzle of each burner is provided with fuel spraying means, Which is an atomizer when liquid fuel is involved. The burner unit 31 is mounted in a wind box 37 which supplies, through the rear open end of the housing 33, the air for combustion of the fuel to the duct of each stage. A stream of primary air passes through the slots in the sleeves 35, a stream of secondary air passes through the ducts and the swirlers 36 therewithin and a stream of tertiary air passes through annular port 38.

An ignitor 41 is disposed centrally between the three stages 32 and a flame viewing tube 42 is disposed adjacent to two of the three stages 32.

The supply of fuel to the burner tubes 34 of the stages 32 is fed through a common conduit 39. The swirlers 36 may, if desired, be provided as a series of adjustable vanes constructed as described in US. Patent No. 2,911,034.

Control of the rate of feed of fuel to the burner tubes 34 may be effected manually or automatically. Withdrawal of the burner unit 31 for or after shut-down may be eifected manually or mechanically, for example, by hydraulic or pneumatic means. Upon retraction of the burner 31 for shut-down, the housing 33 comes to bear against an annular stop 43, so cutting oif the flow of air from the wind box 37. It will be understood that the wind box 37 may feed one or more multi-stage burner units other than the burner unit 31.

The three flames of the three stages 32 virtually merge to form a single flame so that this single flame may be monitored by the viewing tube 42 from within the flame itself in contrast to the normal method of monitoring from the side of the flame. The viewing tube is provided with means, for example a photoelectric cell, which is effective, in known manner, to actuate or otherwise control the igniter and/ or the burner.

PatentedNov. 8, 1966 The burner unit 51 illustrated in FIG. 3 comprises seven stages 52 mounted in a tubular sleeve 53 which is gslidable in a furnace wall 61) in such manner as to be reitractable therefrom to cut off the air supply. Each stage includes a burner tube 54 adapted for spraying fuel, said tube being mounted coaxially within an air duct and surrounded at its forward or nozzle end by a tube or sleeve 55 through which primary combustion air is fed to the fuel. Swirlers 56 are mounted within each air duct at the forward end of each sleeve 55 to swirl the secondary air emerging from the air duct, and the swirlers are provided so that the secondary combustion air of one stage is swirled in a direction opposite to that of the secondary combustion air of an adjacent stage. A stream of tertiary air is fed to the burner unit through an annular port 58. The burner unit includes two ignitor tubes 61 and three flame viewing tubes 62 for monitoring the ignitor tubes and/ or the burner unit.

The fuel spray tubes 54 of the seven stages 52 of the burner unit are fed from a common source of fuel and the combustion air for the ducts of the seven stages is also fed from a common pressure source, such as the wind box illustrated in FIG. 2. The seven individual flames of the seven stages 52, each flame being provided with its own streams of air for combustion, form what is virtually a single flame, namely the flame of the burner unit 51. The ignitor tubes and viewing tubes are provided within this single flame.

Although the individual stages of each of the constructions of burner unit illustrated in the drawings are shown contiguously disposed, it will be understood that the individual stages of a cluster may be spaced apart and that the distance between two adjacent individual stages may be different from the distance between two other adjacent individual stages in the cluster, that is to say, in the burner unit.

I claim:

1. A multi-stage burner unit comprising a housing means slidingly retractable from a furnace wall and positioned in its retracted position to cut off supply of air to the unit, a plurality of individual burner stages arranged in a cluster in said housing, each said stage including an air duct for combustion air, a pressure source of combustion air common to all said stages and connected to each said air duct, a burner within and surrounded by each air duct, a sprayer for fuel associated with each said burner, a source of fuel common to all said stages and connected to each said sprayer, and means in each said duct and about each said burner for etfecting turbulence of combustion air in such Wise that air from one duct is rotated in a direction opposite to that imparted to air from an adjacent duct.

2. A burner unit as claimed in claim 1 in which the individual stages are so arranged in the cluster that combustion in one stage assists combustion in an adjacent stage.

3. A burner unit as claimed in claim 1 in which the means for effecting turbulence of air in each stage comprises a swirler arranged to rotate air about the longitudinal axis of the associated stage.

4. A burner unit as claimed in claim 3 in which each swirler serves to effect turbulence of secondary air for combustion.

5. A burner unit as claimed in claim 1, in which the housing is of circular cross-section.

6. A burner unit as claimed in claim 1, including a monitoring tube.

7. A burner unit as claimed in claim 3, in which each swirler is adjustable.

8. A burner unit as claimed in claim 1, including a path for a stream of tertiary air.

References Cited by the Examiner UNITED STATES PATENTS 1,508,718 9/1924 Peabody 1581.5 2,241,611 5/1941 Mulholland 1581l5 X 3,045,744 7/1962 Tjernlund 158-36 X FOREIGN PATENTS 164,777 1/ 1934 Switzerland.

FREDERICK L. MATTESON, JR., Primary Examiner.

E. G. FAVORS, Assistant Examiner. 

1. A MULTI-STAGE BURNER UNIT COMPRISING A HOUSING MEANS SLIDINGLY RETRACTABLE FROM A FURNACE WALL AND POSITIONED IN ITS RETRACTED POSITION TO CUT OFF SUPPLYOF AIR TO THE UNIT, PLURALITY OF INDIVIDUAL BURNER STAGES ARRANGED IN A CLUSTER IN SAID HOUSING, EACH SAID STAGE INCLUDING AN AIR DUCT FOR COMBUSTION AIR, A PRESSURE SOURCE OF COMBUSTION AIR COMMON TO ALL SAID STAGES AND CONNECTED TO EACH SAID AIR DUCT, A BURNER WITHIN AND SURROUNDED BY EACH AIR DUCT, A SPRAYER FOR FUEL ASSOCIATED WITH EACH SAID BURNER, A SOURCE OF FUEL COMMON TO ALL SAID STAGES AND CONNECTED TO EACH SAID SPRAYER, AND MEANS IN EACH SAID DUCT AND ABOUT EACH SAID BURNER FOR EFFECTING TURBULENCE OF COMBUSTION AIR IN SUCH WISE THAT AIR FROM ONE DUCT IS ROTATED IN A DIRECTION OPPOSITE TO THAT IMPARTED TO AIR FROM AN ADJACENT DUCT. 